1. Field of the Invention
This invention relates to a temperature sensor label, and more particularly, to a temperature sensor label that is affixed to a desired part of various types of apparatus requiring temperature regulation and irreversibly indicates, by means of color change phenomenon, the fact that the temperature of the apparatus has reached or overrun a preset level.
2. Description of Related Art
A temperature sensor label is capable of being affixed easily to a desired part of various types of apparatus and being used in a small space without the need of a power source or the like. For these reasons, such temperature sensor labels are widely used in all kinds of industries to regulate the temperature of the apparatus. The temperature sensor labels are of an irreversible type and a reversible type. The irreversible temperature sensor label changes color to indicate the fact that the temperature of a measured object has reached or overrun a preset level, and continues the same color indication even after the temperature of the measured object has decreased back to the set level or lower. The reversible temperature sensor label changes the color indication in response to the change in the temperature of the measured object.
The irreversible temperature sensor label is used widely, for example, for the temperature regulation of remotely located and unmanned apparatus or apparatus needing to be regularly checked at fixed intervals. There are various types of coloring mechanism for the irreversible temperature sensor label. The currently mainstream type is the coloring mechanism in which colored paper and a sheet-form temperature sensitive material impregnated with a meltable substance melting at a preset temperature are placed on top of each other and a colored face of the colored paper which has been obscured and unseen from the outside shows through because of the melting phenomenon of the meltable substance. In this type, it goes without saying that the meltable substance melting at a preset temperature is a significantly important factor and the meltable substance has a decisive effect on the pass/fail evaluation of sensing accuracy. The irreversible temperature sensor label is of two types, either using chemical substance or using petroleum wax as the meltable substance.
Regarding the type of chemical substance used, chemical substances melting at certain temperatures are pre-selected through experimentation or the like, and then a temperature sensitive material is made properly selectively using a chemical substance suited to the required preset temperature. More specifically, if the preset temperature is 45° C., trilaurin is used. If the preset temperature is 50° C., myristic acid is used. If the preset temperature is 70° C., behenic acid is used. If the preset temperature is 95° C., stearamide is used. In this manner, various chemical substances are selectively used to produce individually suited temperature sensitive materials.
Such a type of temperature sensor label using chemical substances has the advantages of being capable of relatively precisely sensing the temperature and being relatively un-liable to alter its quality even under adverse conditions of use such as under high temperature conditions. However, by reason of the need to prepare various chemical substances differing according to the preset temperatures, there are disadvantages. Just the stock control in the manufacturing location in itself is an onerous task, and therefore the manufacturing costs for the temperature sensor labels are significantly increased.
On the other hand, the type of irreversible temperature sensor label using petroleum wax as the meltable substance has a great advantage of keeping the manufacturing costs considerably below those for the type using the chemical substances. More specifically, petroleum wax is a substance that has been widely used in many kinds of industrial fields through the ages, and the elucidation of its composition and characteristic properties have been developed over time. Due to the consequent accumulation of abundant data, at the present time, the setting of slightly different melting temperatures (melting points) as required is allowed by means of refining treatment and blending. Further, because of significantly easy availability of petroleum wax, it can be said that petroleum wax has outstanding characteristic properties as a meltable substance for the temperature sensor label.
FIG. 1 illustrates a typical example of the type of temperature sensor label using petroleum wax, which is currently commonly manufactured. A waxed paper 2 impregnated with petroleum wax melting at a preset temperature is mounted on a base 1. A colored paper 3 is overlaid on the waxed paper 2 with a colored face 4 thereof facing the waxed paper 2. Then, a transparent film 5 covers the entire front surface. In this temperature sensor label, the colored face 4 of the colored paper 3 is positioned on the rear side so as to be obscured and normally unseen. However, once the temperature reaches a preset level, the petroleum wax with which the waxed paper 2 is impregnated melts and penetrates the colored paper 3 to make it transparent. As a result, the colored face 4 which has been unseen hitherto shows through the front surface, that is, it becomes visible from above to show the change in color.
However, the temperature sensor label using the conventional petroleum wax involves still another problem concerning its weathering properties. That is, if a fracture such as pin-hole occurs in the transparent film 5 for any reason, water enters the inside through the fracture, Thereupon, the water is absorbed by the colored paper 3 itself, or alternatively, is retained between the colored paper 3 and the waxed paper 2. As a result of this, the precise change of coloring at the preset temperature is inhibited.
Further, petroleum wax itself has the property of vaporizing at high temperature. Therefore, when the preset temperature is high, the petroleum wax with which the waxed paper 2 is impregnated vaporizes, though only slightly, so that sufficient change in coloring may not be produced.